It is often necessary to repair pipes, tubes and the like, such as sewer pipes, that are disposed in locations that are difficult or impossible to access. Some such situations are encountered in connection with underground sewer, storm water, potable water, gas, and other utility pipes. As pipes age, they begin to leak or fail structurally and require replacement or repair. Replacing pipes, especially underground, can be extremely difficult and expensive. Accordingly, technologies have been developed to repair pipes in locations that are difficult to access, rather than replace them. One such technology involves the use of cured-in-place pipe liners that can be inserted within old pipes to essentially replace the old pipes. Specifically, cured-in-place pipe liners are known in which a flexible tube (often referred to as a sock or bag) comprising a curable resin disposed on a backing sheet, such as a felt or polymer sheet, is used to line the inner diameter of an old pipe with what will essentially be a new pipe. Cured-in-place pipe liners are very cost effective because they require little or no digging, i.e., access is necessary only at the upstream and downstream ends of the pipe segment to be lined, which commonly are readily accessible through manholes.
Cured-in-place linings for sewer pipes, for example, can be installed in segments of very long lengths, reaching several kilometers, if necessary. However, segments of 360-400 feet between manholes are most common.
Typically, a cured-in-place liner is delivered to the site as a hollow tube with the curable resin on the inside of the tube and the polymer backing on the outside. In some types of cured-in-place lining operations, one end of the sock is closed and the open longitudinal end of the sock is positioned adjacent one end of the pipe segment to be lined. Pressure is then applied to simultaneously evert the sock (so that the resin ends up on the outside and the backing on the inside of the sock) and force the sock into the pipe segment. Other techniques also are known for inserting the liner into the pipe, including, but not limited to pulling the liner with a cable from the downstream end of the pipe segment to be lined, attaching the liner to a pipe crawler that travels down the pipe segment pushing or pulling the liner along with it, and using water tower inversion. When such pushing or pulling techniques are used, the liner does not necessarily need to be closed at one end.
Then, if necessary, one or both ends of the liner are capped to make it air-tight for pressurization. The liner is then pressurized (e.g., from the open end or through a side valve) to cause it to expand to conform to the inner wall of the original, old pipe as well as simultaneously heated to cause an exothermic reaction to cure the liner, thereby forming a new pipe within the old pipe having almost as large a cross-section as the original pipe. The pressurization and heating can be performed by forcing hot water or steam under pressure inside the liner. The specific pressure and heating profile will, of course, depend on the particular resin composition, but an exemplary profile may require heating to between 125° F. and 200° F. at a pressure between 3 psi and 15 psi for between 1 and 1.5 hours. The pressure and heat in the pipe is monitored by pressure and temperature gauges to assure that they both stay within prescribed ranges for a sufficient duration to assure that the exothermic reaction occurs fully to properly cure the resin.
After the resin is properly cured and the liner cools down, any excess liner at one or both ends of the lined pipe segment are cut off to leave an open, newly lined pipe segment.
The resin must be maintained at a certain minimum temperature and pressure for a certain minimum period of time in order to properly cure the resin. However, Applicants have found that significant temperature variations exist along the liner so that a single temperature gauge does not provide sufficient information to confirm that the temperature is within the prescribed range along the entire pipe so to assure proper curing over the entire length of the lining, especially as the lengths of the segment become longer. If the liner is not completely cured over its full length, the entire lining operation may be compromised.
Many factors can contribute to temperature variations within the lining, such as poor heating fluid circulation. Another common cause of temperature variation within the pipe segment is because different portions of a pipe segment may pass through different environments with different thermal coefficients. For instance, one portion of a pipe segment may extend under a roadway while another portion runs under a river and yet another portion is above ground and, therefore, exposed to the cold outside air. The portion under the roadway is likely to be hotter than the portions under the river or exposed to the air because the water in the river or the outside air will act as a much more efficient heat sink (especially in cold weather) than the roadway. If the entire length of the liner has not been properly cured, the entire installation may be at risk of failing. Accordingly, it is important to assure that the entire length of the liner has been cured properly.
Various solutions for monitoring the temperature of the liner at multiple locations along its length have been offered, including placing thermocouples at multiple locations in larger pipes and inserting temperature sensing chips at multiple locations in smaller pipes to monitor the temperature at various locations within the pipe. Such solutions are costly, time consuming and/or labor intensive. They also provide temperature information only at discrete locations and distances along the pipe. Yet further, they are relatively bulky components that commonly remain in the pipe after installation and impede the flow of fluid within the pipe.